The present invention relates to an anti-lock hydraulic brake system for vehicles incorporating a master cylinder and at least one wheel brake connected to the master cylinder. An anti-lock apparatus is provided having sensors for the associated wheel brakes by which, in the event of excessive deceleration of a vehicle wheel, the vehicle wheel will be blocked in relation to the master cylinder by means of a valve and will be connected to a relieving device.
A device for hydraulic brake systems with anti-lock control is known (p 29 08 482.0-21) having a piston sealingly slidable in a bore which, on the one hand, confines an inlet chamber connected to a master cylinder and, on the other hand, confines an outlet chamber communicating with at least one wheel cylinder. The piston includes a passage closable by a valve member and connecting the inlet chamber to the outlet chamber. The valve memer in the final position of the piston, in which the outlet chamber has its smallest volume, is mechanically held open, and the piston is slidable by means of a control piston confining a control chamber for the purpose of enlarging the outlet chamber. A reaction piston designed as a stepped piston confines the inlet chamber, the smaller application surface of the reaction piston facing the inlet chamber and the larger application surface bounding a reaction chamber which is in direct communication with a pressure fluid reservoir. The control piston is arranged on the inlet chamber side of the piston and is connected with same by means of a piston shaft. The control piston confines the reaction chamber and a spring disposed in the control chamber preloads the control piston and the piston in the direction of the outlet chamber, and the reaction piston is arranged on the piston shaft slidably in relation thereto.
In addition to an additional pressure-fluid supply reservoir, this known hydraulic brake system necessitates a pump driven by a motor and a special pressure accumulator, thence permitting to be mounted on comparatively expensive vehicles only. Therefore, it is the object of the present invention to devise an anti-lock hydraulic brake system for vehicles which manages without any special pressure-fluid supply system and thus lends itself to manufacture at particularly low costs.